Fluid-traversed flow piston unit

ABSTRACT

Fluid-traversed flow piston unit, having a housing and pistons for moving in cylinders of an axially mounted rotor and having a control body for controlling the induction with fluid of the cylinders. A coupling body is mounted in a recess of the housing or of a housing part for axial movement. The coupling body is provided with shoulders and at least one eccentric extension so that at least one radial eccentrically extending fluid pressure chamber is formed between the shoulders and a wall of the recess of the housing. In this manner the fluid in the fluid pressure chamber presses the coupling body against the rotor.

United States Patent Eickmann 1 Feb. 26, 1974 FLUID-TRAVERSED FLOWPISTON UNIT 2,932,256 4/1960 Orshansky 91/485 2,80 94 101957 h k [76]Inventor: Karl Elckmann, 2420Issh1k1 9 5 org ans y 92/485 Hayama-machi,Kanagawa-ken, Japan Primary Exammer-W1ll1am L. Freeh AssistantExaminer-Gregory P. LaPointe F1169: s 1971 Attorney, Agent, or FirmTorenand McGeady [21] Appl. No.: 189,598

[57] ABSTRACT [30] Forelgn Apphcat lon Priority Data Fluid-traversedflow piston unit, having a housing and Oct. 22, 1970 Austria 1954/70pistons for moving in Cylinders of an axially mounted rotor and having acontrol body for controlling the in- [52] US. Cl. 91/487 duction withfluid of the cylinders A Coupling body is [51] Int. Cl. F011) 13/04mounted in a recess of the housing or of a housing [58] Field Of Search91/484-489 part for axial movement The coupling body i vided withshoulders and at least one eccentric exten- [56] References C'ted sionso that at least one radial eccentrically extending UNITED STATESPATENTS fluid pressure chamber is formed between the shoul- 3,092,0366/1963 Creighton 91/485 ders and a a f th r ess of the housing. in this3,410,220 12/1968 Kratzenberg et a1. 91/485 manner the fluid in thefluid pressure chamber presses 2,861,552 11/1958 Creighton et al. 91/485the coupling body against the rotor. 2,779,296 l/l957 Dudley 91/4853,043,233 7/1962 Rumsey 91/485 3 Claims, 5 Drawing Figures 5 E 25 [0 5 9H 6 1y l i 1 49 /5 VIII 6 26 I I 3 47- a\ I L 25 5/ /4 J l0 1 /3 /B 2445 11 PAIENTEBFEBZBIQH 3.793.924

sum a *nr 3 I INVENTOR.

KA RL E/CKMANN A 770/? Mt):

PMENIED FEB2 61974 sum 3 or 3 FLUID-TRAVERSED FLOW PISTON UNIT FIELD OFINVENTION The invention relates to a fluid-traversed axial flow pistonunit with pistons which move in cylinders of an axially mounted rotorand having a control body for controlling the admission or induction offluid to the cylinders.

BACKGROUND INFORMATION Such axial flow piston units, particularly axialflow piston pumps, compressors, motors, transmissions and the like, havebeen used successfully for a long time with excellent results in thefield of pneumatics and hydraulics. However, the manufacture of therotors is extremely difficult and expensive in such units. Further, thecontrol is complicated and a positioning angle of the rotor to the driveflange axis can be realized in highpressure units only up to about 25 to30. This sets a limit for the output of the presently known axial flowpiston units, while on the other hand a certain minimum expenditure cannot be reduced.

SUMMARY OF lNVENTlON The object of the invention is to overcome orminimize these disadvantages of the present axial flow piston units andto provide an inexpensive, powerful, dependable and safe axial flowpiston unit of high efficiency and improved output.

The invention resides, therefore, on the one hand, in mounting acoupling body in a housing or cover part of the unit for limited axialmovement, to design the coupling body simply and expediently and topress it against the rotor unit of the axial flow piston machine bymeans of fluid chambers arranged on its rear shoulders. 1

According to another feature of the invention, the entire abovementioned coupling body is associated with an axial-cylinder-rotor withthrough-going cylinders of the same diameter over the entire cylinderlength.

Another feature of the invention consists in dimensioning and placingthe fluid chambers on the shoulders of the coupling body in such a waythat the sealing web between the rotor unit and the control part on thecoupling body or the control part of the coupling body requiresinsignificant radial extension or expansion whereby the frictionsurfaces between rotor and stator are thus reduced, which in turnresults in a reduction of the friction and consequently in an increaseof the efficiency of the unit.

An advantage of the invention is that it is possible, with a suitabledesign of the unit, to increase the positioning angle of the rotor tothe drive shaft from the presently customary 25 to 28 to much largerangles, for example, up to 45 and thus considerably to increase thepiston stroke and the output of the unit, in some cases up to almost 100percent.

A further feature of the invention is the arrangement of fluid pressurefields in the piston walls, arranged tan gentially or in the directionof the thrust-piston, with automatic control of the induction orcharging of the latter by means of bores provided in the piston and bymeans of connecting recesses in the piston rods. This arrangement alsocontributes to enlarging the positioning of the angle of the axial flowpiston unit with simultaneous reduction of the friction between thepistons and cylinders of the unit.

The small positioning angles and the low output of the prior art axialflow chamber units, their extended supporting bearings and sealingsurfaces between stator and rotor, as well as their friction betweenpistons and cylinders, and their construction costs and precisionrequirements, are successfully replaced according to the invention byimproved structural and operating conditions.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this sepcification. For a better understanding of the invention,its operating advantagesand specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

IN THE DRAWINGS FIG. 1 shows a longitudinal section through anembodiment of an axial flow piston unit designed according to theinvention;

FIG. 2 shows a cross-section through FIG. 1 along line 11-";

FlG. 3 is a cross section through a part of the unit of FIG. 1 alongline lIl-lll; and

FIGS. 4 and 5 are partial sectional views taken along the line lV--lV inFIG. 1.

In housing 11 the rotor 12 is rotatably mounted, in a known manner, forexample, in bearings 15 and secured against axial displacement. in therotor are arranged the cylinders 13 in which the pistons 14 slideaxially outwardly and inwardly in order to admit fluid, such as a liquidor gas, into the cylinder or to eject the fluid from the cylinders. Thepistons 14 are driven in known manner by means of the connecting rods orpiston rods 18, the latter being arranged between the pistons 14 and thedrive flange 19. The drive flange 19 has an inclined position to therotor 12 relative to the axial movement; or the pistons drive the driveflange 19 when the unit works as a motor. The drive flange is likewisemounted rotatably in the unit housing 11 by means of the bearings 21, 22and of the holder 23, if necessary. Between rotor 12 and drive flange 19there can be arranged, likewise in known manner, the gearing 16 and 17for synchronizing the rotation of the rotor and of the drive flange. Inthe housing 11 or on the latter can be arranged a cover 24 with thefeedand discharge connections 25 and 26, as it is likewise customary inthe art.

According to the invention, a recess is provided in the housing part orrear cover 24, which has at least two different diameters at differentareas and in which a coupling body 1 according to the invention isarranged for limited movement in axial direction. One part of the recesshas a cylindrical outer surface, which is arranged eccentrically offsetto the cylindrical outer surface of the other part of the recess. Thecoupling body 1 is in turn provided with at least two cylindrical outersurfaces of different diameter which are offset with the sameeccentricity to each other and which are fitted into said twocylindrical inner surfaces of the recess in part or cover 24.

The form or configuration of the above mentioned recesses according tothe invention in the coveror housing part 24 and of the coupling bodyaccording to the invention will be understood best by viewing FIG. 2together with the corresponding part in FIG. 1. As can be seen from FIG.2, the inner surface 9 of the recess, which is equal to the outersurface 9 of the respective part of the coupling body 1, is arrangedeccentrically relative to the center and the outer diameter of housing11 or cover part 24. The eccentricity between the axis of the couplingbody 1, which may be equal to the axis of housing 11 or cover 24 and tothe axis of the respective coupling body part with the outer flange 9,is designated with e in order to clearly identify this importantprerequisite of the invention. As is seen from FIG. 1, the cylindricalsurfaces 9, 8 and are arranged in series in axial direction. They can beseparated from each other by recesses or dividing cut-outs. In FIG. 2,it can clearly be seen from the dash lines representing the cylindricalsurfaces 8 that the cylindrical surfaces 9 are arranged eccentrically tothe cylindrical surfaces 8. The respective cylindrical inner surfaces 8,9 and 10 in housing 11 or cover 24 and the cylindrical outer surfaces 8,9 and 10 on the coupling body 1 are represented in the figures only by aline, because the cylindrical inner surfaces of the coupling body arefitted tightly or strongly in part 1 1 or cover 24, so that no twosurfaces are seen anymore with the naked eye after the assembly of theunit. The fitting of the outer surfaces into the inner surfaces is,however, effected with so much play, that the coupling body 1 can moveeasily in the part 11 or 24 in axial direction by the indicated amount.Frequently packing rings are inserted in the outer surfaces of thecoupling body 1, which are crosshatched in the drawing. These serve toimprove the scaling between the inner surfaces and outer surfaces.Finally, FIG. 1 and FIG. 2 also show that the additional cylindricalinner surface 10 can be provided in cover 24 or in a separate insert244, which surface encloses a corresponding outer surface 10 on thecoupling body 1. The purpose of this arrangement will be explainedlater.

The corresponding parts of the coupling body 1 are somewhat. shorterthan the corresponding recesses in the cover or housing 24, 244 or 11,so that the fluidcontaining fluid chambers 3 and 2 or 3 and 50 can bedesigned according to the invention axially of the respective couplingbody parts. Into the fluid chamber 3 opens the fluid line connection 25and the fluid line 6 passing through the coupling body. Into the fluidchamber 2 opens the line connection 26 and the fluid line 5. These fluidlines are also frequently called cuts or channels. The fluid pressurechamber 50, which will be called hereafter counter-pressure chamber 50,is connected either to the fluid pressure chamber 2 or to the fluidpressure chamber 3. This connection can be effected by means of theducts, or it is effected by corresponding ducts with non-return valvesor reversal switches arranged in the latter. If the counter-pressurechamber 50 is provided, it is necessary that it is connected with therespective fluid-traversed fluid chamber 2 or 3 of the respective higherpressure.

FIGS. 4 and 5 show the alternate arrangements for such connections.

In FIG. 4, one-way valves are demonstrated, while in FIG. 5, thealternate of a flow control valve is illustrated.

In FIG. 4 a fluid passage 331 extends from the chamber 3 to a one-way orcheck valve 332 which is loaded by a spring member 333. Pressure in thechamber 3 causes the check valve 332 to open and pass fluid through thepassage 334 into the counter-pressure chamber 50, if however, thepressure is higher in the counterpressure chamber 50, then the higherpressure acting through line 334 will close the check valve 332.Further, in FIG. 4, a fluid passage 22] extends from the chamber 2 to aone-way valve means 222 retained in place by a spring member 223. Thevalve will open if higher pressure exists in chamber 2 and will passfluid from the chamber 2 into the counter-pressure chamber 50. On thecontrary, if chamber 50 contains the higher pressure, then the higherpressure fluid from chamber 50 will pass through line 224 and cause thevalve 222 to close.

As an alternative, in FIG. 5, a fluid flow control chamber 444 containsa flow control piston 445 which is axially movable in the chamber. Themiddle of the control chamber 444 is in communication with a fluidpassage 443 connected at its other end to the counterpressure chamber50. At one end, the control chamber 444 communicates through a passage441 to chamber 3 and at its other end through a passage 442 itcommunicates with the chamber 2. Accordingly, if a higher pressure fluidis contained within the chamber 3, the fluid control flow piston 445 ismoved to the right, as shown in FIG. 5, to open the passage 443 to thechamber 50 and, if the higher pressure exists within the chamber 2, thepiston 445 is moved in the opposite direction so that chamber 2 andcounter-pressure chamber 50 communicate with one another and are at thesame pressure.

The rotor 12 is secured against axial displacement in the bearings 15.The coupling body 1 or the associated control body bears with its endface 7 or control body arranged on the coupling body on the respectiverotating end face of the rotor 12. The face 7 on the rotor 12 and theface 7 on the coupling body or control body 1, 111 form in known mannerthe control level (German: Steuerspiegel) of the unit. Since suchcontrol levels are known per se, reference is made with regard to theirdescription to the literature. The control body 111, which may beassociated with the coupling body, is shown in broken lines in FIG. 1.If the control body 11 l is not provided, then the respective end of thecoupling body is designed as a control body. The axial length of therecesses and of the coupling body parts are so designed that thecoupling body 1 can move axially to a limited extent toward the rotor 12or away from it. This is necessary so that the proper control leveldistance is always adjusted between the rotating control surface 7 andthe stationary control surface 7.

The diameters of the parts of the coupling body with the outer surfaces9 and 8 and the eccentricity between them are so dimensioned that inunits with reversible direction of rotation, the radial sections throughthe fluid pressure chambers 2 and 3 are of equal size and that it isensured by the eccentricity e between them that one fluid pressurechamber exerts its main pressure over about l of the control level, andthe other exerts its main pressure over the other l80 of the con" trollevel. The rear end of the fluid pressure chamber 3 is bounded andsealed by means of the pin or journal with the cylindrical surfaces 49on the coupling body and on the cover 24 or housing 11. If D is thediameter of the cylindrical surfaces 8, d the diameter of thecylindrical surfaces 49, and R the radius of the cylindrical surfaces 9,then the equal size of the cross-sections through the chambers 2 and 3can be determined by means of the equation The eccentricity e can alsobe determined mathemati cally or fraphically.

1f pre sure fluid flows through the ducts and chambers 3, 6, 25, thefluid chamber 3 presses the coupling body 1 against the rotor in orderto seal the control level 7. If fluid pressure prevails in chamber 2, orfluid pressure flows through the ducts 2, 5, 26, the fluid pressure inchamber 2 presses the coupling body 1 against the rotor 12 to seal thecontrol level 7.

According to the invention, the dimensions of the diameters 8, 9 or 10and 49 can be so reduced so that no extended support bearings have to bearranged between rotor 12 and coupling body 1 or control body 111.Narrow packing strips or webs in control level 7 suffice, since thepressure of the coupling body 1 against the rotor 12 can be veryaccurately dosed by the invention.

Due to the possibility of accurately dosing the bearing or contactpressure of the coupling body according to the invention against therotor and the resulting pos' sibility of reducing the sealing surfacesand/or bearing surfaces in the control level, friction is saved and theefficiency of the machine is thus considerably increased.

The exact adaptability of the diameter conditions of the coupling bodyaccording to the invention and thus of its contact pressure on the rotorhas also made it possible to provide the rotor 12 in a simple mannerwith cylinders of the same kind, because the coupling body can be sodimensioned that it can just counteract the fluid force from thecylinder openings. The rotor 12 can thus be made shorter and theproduction of the rotor 12 with cylinder throughbores is much simplerthan the designs with cylinder bores which do not traverse the entirerotor. The rotor manufacture thus becomes much simpler and lessexpensive by the control or coupling body arrangement according to theinvention.

Since the rotor is no longer pressed against the control body accordingto the invention, but, in the reverse, the coupling body is pressed in asimple manner against the rotor, the rotor 12 can be fixedly mounted inthe bearings 15 and the rotor 12 can thus be imparted with a largepositioning angle without impairing the safety of the unit. This permitsvery long piston strokes and consequently a high output in the unitaccording to the invention.

Due to the wide positioning angle of the rotor to the drive flange axis,force components are produced by the piston rods 18 on the outer pistonwalls and the walls of the cylinders 13 which are greater than in axialflow piston machines with smaller angles and lower outputs. In order tocompensate for these force components, pressure fluid fields (recesses)31 and 311 to 315 can be provided in the walls of the pistons 14, whichextend in the direction of the axis of the connecting rods or thrustpistons and in which a fluid force is built up which counteracts theforce component of the connecting rods 18 on the pistons 14. Thispermits radial forcefree floating of the pistons 14 in the cylinders 18,which in turn reduces the friction between piston walls and cylinderwalls. To this end a simple control of the induction of these pressurefluid chambers is provided.

As can be seen from HO. 3 and FIG. 1, at least one recess, butpreferably a number of recesses 31, 311, 321, 313, 314, 315 or the likeare worked in the pistons 14 radially from the outside. Through thepiston 14 extends the bore 34. In the head of connecting rod 18 isprovided, inside the piston 14, a customary flattening or cut-out of thespherical head, as it is also possible in the known axial flow pistonunits. A small fluid pressure chamber is thus formed between theconnecting rod head and the piston, which is filled with compressedfluid from the respective cylinder through bore 34. According to theinvention, a bore or a duct 32, 321-325 extends from each fluid pressurecut-out 31 or 311 to 315 up to the seat of the connecting rod head inthe respective piston 14 and opens into the latter. Tl-le radialdistance of these bore openings from the piston axis and the diameter ofthe connecting rod head or recess in the piston head are so dimensionedthat, with greater positioning angle of the connecting rod to the pistonaxis, the flattening or cut-out on the connecting rod head establishes aconnection between the piston bore 34 and one or several of the ducts32, 321, 322, 323, 324, 325, while the connection to the other of theseducts remains closed by the connecting rod head. According to theinvention it is thus made sure in this way that the fluid pressurefields 31 in piston 14 are charged with fluid pressure which are just inthe extension of the connecting rod axis of the respective connectingrod or rods 18. lt is then no longer the piston surface that pressesagainst the cylinder wall in the direction of the connecting rod axis,but the fluid in the respective fluid pressure chamber 31 or 311 to 315.Actually a fluid film is, of course, also formed between the remaindersof the surface of the respective pistons and the cylinder walls in whichthe pressure decreases with a certain pressure gradient with increasingdistance from the pressure fluid chamber. The conditions in this filmmust be taken into account in the calculation of the size and positionof the pressure fluid pockets 31, 311, 312, 313, 314 and 315. In thisway the friction between the walls of the pistons 14 and the inner wallsof the cylinders 13 is substantially reduced according to the inventionand a larger positioning angle may be used between the piston axis andthe drive flange axis, and thus a long piston stroke even for high fluidpressures, and a high output in the axial flow piston unit are achieved.The present measures with similar aims, as they are known from theliterature, demonstrate the importance of realizing this aim for highpressures and positioning angles, but the prior art has not disclosedsufficiently simple and exact means for realizing this aim rationally,safely and simply.

From FIG. 2 and the corresponding part of FIG. 1 it can also be seenthat the respective fluid pressure chambers 2 and 3 extend with a largersurface over one half of the control level and with a smaller surfaceover the other half of the control level 7. This is realized, on the onehand by the eccentricity e between the center line of the surfaces 49,8, 10 and the center line of the surfaces 9, on the other hand. In FIG.2, the fluid pressure chamber 2 is arranged between the cylindersurfaces 8 and 9, and the fluid pressure chamber 3 between the cylindersurfaces 9 and 49. The larger surface cross-sections of thefluid-pressure chambers 2 and 3 press in the range of the high-pressurehalf of the control level against the rotor while the smaller surfacecross-sections press against the low-pressure half of the control level7. With lower and medium pressures, this said coupling body having anouter cylindrical surface type is suitable, because the coupling body 1must also extending in the axial direction of said rotor from said bepressed against the rotor 12 in the respective lowend face and saidcylindrical surface comprising a first pressure half of the controllevel 7 and in the reversing cylindrical surface extending from said endface, a seczones Of the lat r. 5 nd cylindrical surface extending fromthe transverse At high or very high fluid pressures and/0 rotor planecontaining the end of said first cylindrical surface speeds it isadvisable, however, to ensure that the couspaced f id d f d S id secondlind ic l pling y 1 is not Pressed too much against the rotorsufiacedisposed concentricallyof "S56E81 cylindri- A too great pressurerepresents a risk for the safety of ca] Surface, and a third cyhndricalSurface extending the unit, particularly in the respective low-pressurehalf 10 outwardly from the transverse plane containing the of thecontrol level 7, because the control surfaces may end of said secondcylindrical Surface Spaced run "1 here, m he welded or hused each otherwardly from said first cylindrical surface and said under cxcesswe h Fori rehsoh the Counter third cylindrical surface being eccentric to saidfirst pressure chamber 50 arranged m hlgh'pressure and second surfacesand having a diameter less than els according to the invention on ashoulder of the couthe diameter of Said Second cylindrical surface plingbody on the rotor i and is connected the so that said third cylindricalsurface is disposed inabove igh z h $3 erkof the h'gher wardly from saidsecond cylindricai su rface, said 5011s pressure "L e ac g i irlg havingsurfaces in closely contacting relationship pressure c am er g t e Cy erwith said first second and third cylindrical surfaces of surfaces 8 andrepresmed m 2 m i i said coupling body, a first shoulder formed on saidcou- The CmSs'.Secuon of this chambefr ls so dlmensloned pling body inthe transverse plane between said first that the fluid pressure from thefluid pressure chambers and second cylindrical Surface; a SecondShoulder 2 and 3 or 2 or 3, so that the resulting contact pressureformed on said couplin bod the transverse lane of the coupling body 1against the rotor just correg y p sponds to the desired optimumconditions. By the posibetween Said Second and thud .cylmdngal Surfacesand tion and dimension of the backor counter-pressure a thud shoulderformed on sand Couplmg body on an chamber 50 it is also possible toarrange the center of Outer end of said third cylindrical Surface saidSecond the pressure of the Coupling body 1 so that it is just shoulderand said third shoulder each combining with close to the fluid pressurecenter in the control gap or Said h h and each forming a radiallyelxtehdihg f' level 7. The counter-pressure chamber according to thecehmc h E r chamber arranged h h" invention permits thus a very simple,very accurate and Canon t e fluld passages through couphhg sensitiveadaption of the contact pressure of the control body so that pressurizedfluid enters said eccentric fluid body or coupling body 1 to therespective conditions in phessure chamhers and Presses the end face thecomm] level 7. pling body against the uxtaposed end face of said ro- Theinvention is not limited to the embodiment tor, and said first shoulderand said housing combining shown in the figures, it is merely limited bythe followto form. cohmer'pressure chamber, and {11621115 for m claimsconnecting said counter-pressure chamber with at least I claim: one ofsaid pressure chambers so that the fluid pressure I. Fluid-traversedaxial flow piston unit comprising a afjmltted to Said 'pf Chamberaffords a housing, a rotor rotatably mounted within said housing 40blasfng effect said coupling y in the pp d secured against i ldisplacement, a p|ura|ity f rection to said biasing effect within saidpressure chamcylinders arranged within said rotor and extending inbersthe axial direction thereof, pistons positioned withinFluid-tfavafsed aXial W pi ton unit, as set forth said cylinders fordisplacement in the axial direction, in claim 1, wherein said housingCombining with Said said housing forming a recess extending outwardly pg to form Said Pressme chambers and Said from one end of said rotor, acoupling body positioned counter-pressure chamber includes a coverlaterally within the recess in said housing and having fluidpasenclosing aid c upling body and retaining said cousages therethroughfor controlling the flow of fluid to pling body within the recess insaid housing.

and from said cylinders, wherein the improvement 3. Fluid-traversedaxial flow piston unit, as set forth comprises that said coupling bodyis arranged within in claim 1, wherein said coupling body includes aconthe recess in said housing for movement in the axial ditrol bodypositioned between the transverse end face of rection of said rotor,said coupling body having an end said rotor and the adjacent transverseend face of said face transverse to the axial direction of said rotorand coupling body.

juxtaposed to the adjacent transverse face of said rotor, a

Mm V ,7

1. Fluid-traversed axial flow piston unit comprising a housing, a rotorrotatably mounted within said housing and secured against axialdisplacement, a plurality of cylinders arranged within said rotor andextending in the axial direction thereof, pistoNs positioned within saidcylinders for displacement in the axial direction, said housing forminga recess extending outwardly from one end of said rotor, a coupling bodypositioned within the recess in said housing and having fluid passagestherethrough for controlling the flow of fluid to and from saidcylinders, wherein the improvement comprises that said coupling body isarranged within the recess in said housing for movement in the axialdirection of said rotor, said coupling body having an end facetransverse to the axial direction of said rotor and juxtaposed to theadjacent transverse face of said rotor, said coupling body having anouter cylindrical surface extending in the axial direction of said rotorfrom said end face and said cylindrical surface comprising a firstcylindrical surface extending from said end face, a second cylindricalsurface extending from the transverse plane containing the end of saidfirst cylindrical surface spaced from said end face and said secondcylindrical surface having a greater diameter and disposedconcentrically of said first cylindrical surface, and a thirdcylindrical surface extending outwardly from the transverse planecontaining the end of said second cylindrical surface spaced outwardlyfrom said first cylindrical surface and said third cylindrical surfacebeing eccentric to said first and second surfaces and having a diameterless than the diameter of said first cylindrical surface so that saidthird cylindrical surface is disposed inwardly from said secondcylindrical surface, said housing having surfaces in closely contactingrelationship with said first second and third cylindrical surfaces ofsaid coupling body, a first shoulder formed on said coupling body in thetransverse plane between said first and second cylindrical surfaces, asecond shoulder formed on said coupling body at the transverse planebetween said second and third cylindrical surfaces and a third shoulderformed on said coupling body on an outer end of said third cylindricalsurface, said second shoulder and said third shoulder each combiningwith said housing and each forming a radially extending eccentric fluidpressure chamber arranged in communication with the fluid passagesthrough said coupling body so that pressurized fluid enters saideccentric fluid pressure chambers and presses the end face of saidcoupling body against the juxtaposed end face of said rotor, and saidfirst shoulder and said housing combining to form a counter-pressurechamber, and means for connecting said counter-pressure chamber with atleast one of said pressure chambers so that the fluid pressure admittedto said counter-pressure chamber affords a biasing effect on saidcoupling body in the opposite direction to said biasing effect withinsaid pressure chambers.
 2. Fluid-traversed axial flow piston unit, asset forth in claim 1, wherein said housing combining with said couplingbody to form said pressure chambers and said counter-pressure chamberincludes a cover laterally enclosing said coupling body and retainingsaid coupling body within the recess in said housing.
 3. Fluid-traversedaxial flow piston unit, as set forth in claim 1, wherein said couplingbody includes a control body positioned between the transverse end faceof said rotor and the adjacent transverse end face of said couplingbody.